1. Field of the Invention
The present invention relates to a water electrolysis system.
2. Discussion of the Background
Recently, a system for supplying an electric power or power using hydrogen as a fuel, for example, a fuel-cell system has been proposed. The type of system employs a water electrolysis apparatus that electrolyzes water and generates hydrogen (and oxygen) in producing hydrogen as a fuel.
The water electrolysis apparatus uses a solid polymer electrolyte membrane (ion exchange membrane) to electrolyze water and generate hydrogen (and oxygen). Electrode catalytic layers are provided at opposite surfaces of the solid polymer electrolyte membrane to form an electrolyte membrane electrode assembly, and an anode-side feed and a cathode-side feed are disposed at both sides of the electrolyte membrane electrode assembly. This configuration forms a unit.
The above-described water electrolysis apparatus produces hydrogen containing moisture, and thus it is necessary to remove the moisture from the hydrogen to obtain hydrogen in a dry state, for example, at or below 5 ppm (hereinafter referred to also as dry hydrogen). One known example of a technique that meets such a need is a solid polymer water electrolysis hydrogen production device disclosed in Japanese Unexamined Patent Application Publication No. 2005-187916.
This hydrogen production device includes a water electrolysis layer 1 that electrolyzes water using a polymer electrolyte membrane and generates oxygen at the anode and hydrogen at the cathode, a hydrogen gas-liquid separator 2 that separates the hydrogen generated at the cathode and water, an oxygen gas-liquid separator 3 that separates the oxygen generated at the anode and water, a water circulation line 4 that supplies water to the water electrolysis layer 1, a hydrogen line 6 provided to the hydrogen gas-liquid separator 2 and including a flow control valve 5a, and an oxygen line 7 provided to the oxygen gas-liquid separator 3 and including an oxygen pressure control valve 5b. 
This type of system employs a high-pressure water electrolysis system that generates high-pressure hydrogen (e.g., at approximately 35 MPa) from the water electrolysis layer 1.